1. Field of the Invention
The present invention is related to vapor separators, and more particularly to vapor separators for fuel systems of marine engines.
2. Related Art
Fuel vapor is a long recognized issue in the marine fuel industry. Small outboard marine engines, including transom mounted and stern drive units frequently utilize an integrated fuel system which draws liquid fuel under suction from a can or tank located in the boat. The fuel is drawn under suction because boat safety regulations require that fuel routed between the tank and engine be sucked under a vacuum to prevent fuel from spilling into the boat should the fuel line rupture. However, the fact that fuel is withdrawn from the tank at a negative pressure can be problematic because, at such low pressures, the fuel can readily evaporate. This, combined with the vapor-producing effects of high temperatures and jarring conditions, could lead to vapor lock and diminished pumping efficiencies if not addressed.
The excessive vapor issue is typically addressed by routing the fuel through a fuel vapor separator unit and then delivering it at a high pressure to the fuel injection system of the engine. In addition to the naturally arising vapors from the vacuum drawing steps, unused, hot fuel from the fuel rail is returned to the vapor separator where fuel vapors are condensed back to liquid before the fuel is reintroduced to the high pressure pump and fuel rail. Uncondensed fuel vapors can be vented to atmosphere or pulled into the engine intake system through a vacuum line connection.
FIGS. 1 and 2 generally depict an outboard marine engine 12 affixed to the transom 14 of a boat, as described more fully in Applicant's U.S. Pat. No. 7,503,314, the entire disclosure of which is hereby incorporated by reference. Outboard marine engines 12 of this type are often mounted to a bracket 16 so that the engine 12 can be quickly removed from the boat for transportation and/or maintenance. The bracket 16 in this example allows the motor head to be rotated about axis A launching, shallow conditions maneuvering, and trim control.
An engine of the type shown in FIG. 1, as well as other marine engine types, commonly run on a liquid fuel like gasoline or ethanol. Liquid fuel is drawn from a fuel tank 20 by an engine-mounted marine fuel system, such as the system generally shown at 22 in FIG. 2. Except for the fuel tank 20 and a supply line 24, the remainder of the fuel system 22 is typically (but not necessarily) integrated into the engine 12.
In operation, a low pressure fuel supply pump 26 sucks fuel from the tank 20 through the supply line 24. The fuel is delivered to a vapor separator, generally indicated at 28. The vapor separator 28 collects and discharges vapors given off from the incoming low pressure fuel and also from the hot, agitated fuel returning from the engine 12. A high pressure pump 30 then pumps the fuel under pressure into the fuel injector system 32 to be consumed by the engine. Unused fuel is returned to the vapor separator 28 via return line 34. A vent valve device, generally indicated at 36, may be provided for connection to the engine intake vacuum system. The vacuum system creates a negative pressure in the vent line 40 so that fuel vapors can be cycled through the engine 12.
The low pressure fuel supply pump 26, also known as a lift pump, may be of the pulsed diaphragm type or any other suitable type. Diaphragm type fuel pumps are sometimes preferred in these applications because they are less susceptible to pumping problems when the fuel is hot and there is a high vapor concentration. Typically, these pulsed diaphragm pumps are operated by air pressure fluctuations generated in the crank case portion of the engine 12. One exemplary pulse pump is shown in Applicant's own U.S. Pat. No. 6,158,972, which is incorporated herein by reference in its entirety.
FIG. 3 shows a simplified, cross-sectional view of one known type of fuel vapor separator assembly 28′. The lift pump 26′ is of the diaphragm type but not energized by engine pulses. Rather, an electro-mechanical device is used to reciprocate a diaphragm (not shown) within the lift pump 26′ to generate the vacuum. The electro-mechanical device may be a linear motor (e.g., a solenoid), a rotating shaft motor, or any other type of electro-mechanical machine. Fuel is drawn, under vacuum, from a tank (not shown) through the supply line 24′ and discharged into the interior of the fuel vapor separator assembly 28′ via inlet 50′. Hot fuel returning from the fuel injectors via return line 34′ also enters the interior of the vapor separator assembly 28′ and intermingles with fuel delivered from the lift pump 26′. A cooling tube 52′ is positioned inside the vapor separator 28′ for the purpose of exchanging heat and reducing the temperature of fuel inside the vapor separator 28′. A continuous supply of water is fed through the cooling tube 52′ from an inlet 54′ to an outlet 56′. A vapor vent 35′ allows fuel vapors to be drawn out of the fuel vapor separator 28′. A high pressure pump 30′ draws fuel from a fuel intake 42′ and discharges the fuel through an outlet 44′ to the fuel injection system of the engine.
Considering the lift pump 26′ in greater detail, FIG. 3 shows an power source 60′ for powering the electro-mechanical device inside the lift pump 26′. A manual prime lever 62′ may be included for the purpose of manually priming the lift pump 26′ in appropriate circumstances.
As will be understood by those of skill in the art, many known vapor separators, such as those described above in connection with FIGS. 2 and 3, use a float/needle assembly 36, 36′ for fuel vapor out control and/or fuel inlet control. However, such float/needle assemblies 36, 36′ are susceptible to wear and leakage. Alternative concepts have been developed using electronic sensors (not shown) disposed inside of the vapor separator unit which require routing wires through the separator housing some form of pass-through sealed connector. Such pass-through sealed connectors often leak and can be associated with common failure modes.